WM8720
Production Data
The MUTE pin behaves as a bi-directional function, that is, as an input to select mute or NOT-mute,
or as an output indication of automute operation. MUTE is active high; taking the pin high causes the
filters to soft mute, ramping down the audio signal over a few milliseconds. Taking MUTE low again
allows data into the filter.
The automute function detects a series of zero value audio samples of 1024 samples long being
applied to both left and right channels. After such an event, a latch is set whose output (automuted)
is wire OR’ed through a 10kohm resistor to the MUTE pin. Thus if the MUTE pin is not being driven,
the automute function will assert MUTE.
If MUTE is tied low, automute is overridden and will not mute. If MUTE is driven from a source
follower, or diode, then both mute and automute functions are available. If MUTE is not driven,
automute appears as a weak output (10k source impedance) so can be used to drive external
mute circuits.
The automute signal is AND’ed with IZD, this qualified mute signal then being OR’ed into the
SOFTMUTE control. Therefore, in software mode, automute operation may be controlled with IZD
control bit.
I2S INPUT FORMAT SELECTION AND IWL INPUT FORMAT SELECTION
In hardware mode, pins 4 and 5 become input controls for selection of input data format type, and
input data word length, see Table 4. I2S mode is designed to support any word length provided
enough bit clocks are sent.
ML/I2S – PIN 4
MC/IWL – PIN 5
INPUT DATA MODE
16-bit normal
20-bit normal
24-bit normal
I2S mode
0
0
1
1
0
1
0
1
Table 4 Control of Input Data Format Type and Input Data Word Length
DM DE-EMPHASIS
In hardware mode, pin 6 becomes an input control for selection of de-emphasis filtering to be
applied. See Figure 8.
DM
0
1
De-emphasis off
De-emphasis on
DM
Table 5 De-emphasis Control
PWDN POWERDOWN CONTROL
In both hardware and software modes, this pin selects powerdown of the entire device when taken
high.
PWDN
PWDN
0
1
Device powered up
Device powered down
Table 6 Powerdown Control
SOFTWARE CONTROL INTERFACE
The WM8720 can be controlled using a 3-wire serial interface. MD/DM (pin 6) is used for the program
data, MC/IWL (pin 5) is used to clock in the program data and ML/I2S (pin 4) is use to latch in the
program data. The 3-wire interface protocol is shown in Figure 7.
ML/I2S
MC/IWL
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
MD/DM
Figure 7 3-Wire Serial Interface
PD Rev 4.0. February 2005
11
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
